Commit 2021-03-09 21:43 9ff74582

feat(algebra/group_power/basic): add abs_add_eq_add_abs_iff (#6593) I've added

lemma abs_add_eq_add_abs_iff {α : Type*} [linear_ordered_add_comm_group α]  (a b : α) :
  abs (a + b) = abs a + abs b ↔ (0 ≤ a ∧ 0 ≤ b ∨ a ≤ 0 ∧ b ≤ 0)

from lean-liquid. For some reasons I am not able to use wlog hle : a ≤ b using [a b, b a] at the beginning of the proof, Lean says unknown identifier 'wlog' and if I try to import tactic.wlog I have tons of errors.